カスタム関数を使用して Matplotlib の棒グラフにグループ ラベルを追加するにはどうすればよいですか?

# Custom function to group data for bar chart
def mk_groups(data):
    newdata = data.items()
    thisgroup = []
    groups = []
    for key, value in newdata:
        newgroups = mk_groups(value)
        if newgroups is None:
            thisgroup.append((key, value))
        else:
            thisgroup.append((key, len(newgroups[-1])))
            if groups:
                groups = [g + n for n, g in zip(newgroups, groups)]
            else:
                groups = newgroups
    return [thisgroup] + groups

# Custom function to label group bars
def label_group_bar(ax, data):
    groups = mk_groups(data)
    xy = groups.pop()
    x, y = zip(*xy)
    ly = len(y)
    xticks = range(1, ly + 1)

    ax.bar(xticks, y, align='center')
    ax.set_xticks(xticks)
    ax.set_xticklabels(x)
    ax.set_xlim(.5, ly + .5)
    ax.yaxis.grid(True)

    scale = 1. / ly
    for pos in xrange(ly + 1):  # change xrange to range for python3
        add_line(ax, pos * scale, -.1)
    ypos = -.2
    while groups:
        group = groups.pop()
        pos = 0
        for label, rpos in group:
            lxpos = (pos + .5 * rpos) * scale
            ax.text(lxpos, ypos, label, ha='center', transform=ax.transAxes)
            add_line(ax, pos * scale, ypos)
            pos += rpos
        add_line(ax, pos * scale, ypos)
        ypos -= .1


# Example usage
data = {'Room A':
                   {'Shelf 1':
                       {'Milk': 10,
                        'Water': 20},
                    'Shelf 2':
                       {'Sugar': 5,
                        'Honey': 6}
                   },
            'Room B':
                   {'Shelf 1':
                       {'Wheat': 4,
                        'Corn': 7},
                    'Shelf 2':
                       {'Chicken': 2,
                        'Cow': 1}
                   }
           }

fig = plt.figure()
ax = fig.add_subplot(1, 1, 1)
label_group_bar(ax, data)
fig.subplots_adjust(bottom=0.3)
# Save the plot to a file
fig.savefig('labeled_group_bar_chart.png')